Electrophoretic display device

ABSTRACT

An electrophoretic display device is described. The device includes a substrate, first electrodes, an electrophoretic film having electrophoretic particles, and second electrodes. The substrate is has a plurality of pixel regions. First electrodes are disposed respectively on each pixel region, and include first patterns separated from one another and second patterns connected to the first patterns. The second electrode is disposed on the electrophoretic film. The area of one of the electrodes, opposing the other of the electrodes has apertures formed therein, reducing the contact area between the electrode and the electrophoretic film.

The present patent document is a divisional of U.S. patent applicationSer. No. 11/601,224, filed Nov. 17, 2006, which claims priority toKorean Patent Application No. 110511/2005 filed in Korea on Nov. 18,2005, which is hereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The present application relates to an electrophoretic display device.More particularly, the present application relates to an electrophoreticdisplay device capable of reducing leakage, and increasing a voltageholding ratio.

2. Discussion of the Related Art

Flexible displays such as “electronic paper” may be formed withelectrophoretic materials. Compared to LCD, plasma or other similar flatdisplay devices, electrophoretic display devices have the characteristicthat they retain their images after power is turned off. Thus, sincepower needs to be supplied to an electrophoretic display device onlywhen switching the displayed image, such devices may be used forelectronic paper that needs to retain an image over a prolonged timeperiod.

FIG. 1A is a plan view of a unit pixel of an electrophoretic displaydevice. FIG. 1B is a sectional view taken along a line I-I′ in FIG. 1A.A plurality of gate lines 11 and data lines 12 are disposed to intersecton a substrate 10, thereby forming a pixel region on the substrate 10.In addition, common lines 13 are formed in parallel with the gate line11 on the substrate 10. The common lines 13 are spaced apart from thegate lines 11 by a predetermined interval.

A thin film transistor Tr is disposed within the pixel region. The thinfilm transistor Tr includes a gate electrode 21 electrically connectedto the gate lines 11, an active layer 23 insulated from the gateelectrode 21, a source electrode 24 a electrically contacted on theactive layer 23 and electrically connected with the data lines 12, and adrain electrode 24 b electrically contacted on the active layer 23 andspaced apart from the source electrode 24 a.

A capacitor lower electrode 14 electrically connected to the commonlines 13 and a capacitor upper electrode 15 electrically connected tothe drain electrode 24 b are formed within the pixel region. Thecapacitor upper electrode 14 is overlapped with the capacitor lowerelectrode 15. An insulating layer is interposed between the capacitorupper electrode 15 and the capacitor lower electrode 14 to form astorage capacitance there between. A first electrode 50 is electricallyconnected to the drain electrode 24 b of the thin film transistor Tr.

An electrophoretic film 60 and a second electrode 70 are disposed on thefirst electrode 50. The electrophoretic film 60 includes electronic inkthat moves by means of electric fields, and a polymer.

The electronic ink formed in the electrophoretic film 60 is driven by anelectric field formed between the first electrode 50 and secondelectrode lines 70 to display an image from the electrophoretic displaydevice.

In order to act as electronic paper, the electrophoretic display devicemust retain an image over a prolonged duration, and the electrophoreticdisplay device requires a high voltage holding ratio. The voltageholding ratio is a charging voltage ratio over time of a signal voltagefirst applied to the electrophoretic display device, and the next signalvoltage applied thereto. The voltage holding ratio is affected by thesurface resistance of the electrophoretic film 60.

Table 1 below shows simulation results of voltage holding ratiosparametric in the surface resistances of the electrophoretic film 60.

TABLE 1 Surface Resistance (Ω/μm²) 10⁹ 10¹⁰ 10¹¹ 10¹⁵ 10²¹ VoltageHolding Ratio (%) 6.08 75.4 97 99.7 99.7

As the surface resistance of the electrophoretic film 60 increases, thevoltage holding ratio of the electrophoretic display device alsoincreases.

When the contacting area between the surface of the electrophoretic film60 and the conductive first electrode 50 increases, the surfaceresistance of the electrophoretic film 60 decreases, and the voltageholding ratio of the electrophoretic display device also decreases. Whenthe voltage holding ratio of the electrophoretic display device is thuslowered, the image on the electrophoretic display device may fade.Moreover, when the surface resistance of the electrophoretic film 60 isreduced, an increase of leakage voltage at the interface between theelectrophoretic films 60 and the first electrode 50 results.

BRIEF SUMMARY

An electrophoretic display device with a high voltage holding ratio isdescribed. The electrophoretic display device may include: a substratehaving a pixel region and a first electrode disposed on the pixelregion, where the first electrode may have a plurality of first patternsseparated from each other on the pixel region; a second patternelectrically connected to two or more of the first patterns. Anelectrophoretic film including electrophoretic particles may be disposedon the first electrode. A second electrode may be disposed on theelectrophoretic film.

In another aspect an electrophoretic display device may include asubstrate having a pixel region and a first electrode disposed on thepixel region and having at least one aperture therein that exposes thesubstrate. An electrophoretic film may be disposed on the firstelectrode and include electrophoretic particles. A second electrode maybe disposed on the electrophoretic film.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate examples of the invention Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

In the drawings:

FIG. 1A is a plan view illustrating an electrophoretic display deviceaccording to the related art;

FIG. 1B is a sectional view taken along a line I-I′ in FIG. 1A;

FIG. 2A is a plan view illustrating an electrophoretic display deviceaccording to the first example;

FIG. 2B is a sectional view taken along a line II-II′ in FIG. 2A;

FIGS. 3A through 3C are graphs showing the equipotentiality of the gapsbetween the first patterns.

FIGS. 4A and 4B are plan views illustrating two configurations of firstelectrodes that may be applied to the electrophoretic display device;

FIG. 5A is a plan view illustrating an electrophoretic display deviceaccording to the second example;

FIG. 5B is a sectional view taken along a line III-III′ in FIG. 5A; and

FIGS. 6A and 6B are plan views illustrating two configurations of firstelectrodes that may be applied to the electrophoretic display of thesecond example.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

Examples of the invention may be better understood with reference to thedrawings, but these examples are not intended to be of a limitingnature. Rather, the invention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention which is set forth by the claims.

FIG. 2A is a plan view illustrated a unit pixel of first example of anelectrophoretic display device, and FIG. 2B is a sectional view takenalong a line II-II′ in FIG. 2A.

The electrophoretic display device includes a first electrode 500, anelectrophoretic film 600, and a second electrode 700. The firstelectrode 500, the electrophoretic film 600, and the second electrode700 may be formed on a substrate 100. A plurality of gate lines 110 anddata lines 120 are disposed to intersect on a substrate 100 so that aplurality of pixel regions are formed on the substrate 100, one of whichis illustrated.

The substrate 100 may include a flexible material. The substrate 100,for example, may be a glass substrate, plastic substrate, or stainlesssteel substrate, or other suitable materials.

The first electrode 500 includes a first pattern 500A and a secondpattern 500B. A plurality of first patterns 500A are spaced apart fromeach other by a predetermined interval and the second pattern 500B iselectrically connected to each of the first patterns 500A. Each of thefirst patterns 500A, for example, is arranged in parallel with the dataline 120. The second pattern 500B is arranged in perpendicular to thefirst patterns 500A. In this example, the second pattern 500B isoverlapped with the first patterns 500A and the second pattern 500B isin parallel with the gate lines 110.

Since the plurality of the first and second patterns 500A and 500B ofthe first electrode 500 are formed within the pixel region a contactingarea between the first electrode 500 and an electrophoretic film 600 isdecreased. Therefore, the voltage holding ratio of the electrophoreticdisplay device may be increased. That is, when the contacting areabetween the electrophoretic film 600 and the conductive first electrode500 is reduced, the surface resistance of the electrophoretic film 600increases to improve the voltage holding ratio of the electrophoreticdisplay device. In addition, a leakage current that may occur at aboundary between the electrophoretic film 600 and the first electrode500 may be reduced as the surface resistance of the electrophoretic film600 increases.

Table 2 shows the simulation results of a voltage holding ratio as afunction of the gap distance (d1) between the first patterns 500A.

TABLE 2 Gaps (μm) Between First Patterns 2 3 4 5 6 Voltage 94.8% 95.395.6 95.8 96 Holding Ratio (%)

As shown in Table 2, when there is a gap (d1) of 3 μm between the firstpatterns 500A, the voltage holding ratio of the electrophoretic displaydevice was 95% or higher.

FIGS. 3A through 3C are graphs showing the equipotentiality of the gapsin the first patterns. Here, FIG. 3A is a graph showing theequipotentiality of the gaps between the first patterns when they are 5μm. FIG. 3B is a graph showing the equipotentiality of the gaps betweenthe first patterns when they are 10 μm. FIG. 3C is a graph showing theequipotentiality of the gaps between the first patterns when they are 15μm.

Referring to FIGS. 3A through 3C, when the gap (d1) between the firstpatterns 500A increases, the voltage ratio in the gap between the firstpatterns 500A becomes lower. When the gap between the first patterns500A is 15 μm, the voltage ratio decreases, and the response of theelectronic ink display may slow down, and the resolution of the devicemay deteriorate.

Therefore, the separation distance d1 of adjacent two first patterns500A may be about 3 μm to about 10 μm. When the distance d1 between thefirst patterns 500A is less than about 3 μm, the decrement of the areaof the first electrode 500 is small and a small effect on increasing thevoltage holding ratio. When the distance d1 between the neighboringfirst patterns 500A are greater than about 10 μm, the electrophoreticparticles in the electrophoretic film between the first patterns 500Amay be poorly driven. A length L1 of the first patterns 500A is formedwith the same length as, or a shorter length than, the distance d1between the first patterns 500A, so that all of the electrophoreticparticles in the electrophoretic film of a pixel may be driven,resulting in a uniform image formation.

The first electrode 500 may include a transparent conductive materialand a reflective conductive material. The transparent conductivematerial may be indium tin oxide (ITO) or indium zinc oxide (IZO), forexample. The reflective conductive material may be platinum (Pt), gold(Au), Iridium (Ir), chromium (Cr), magnesium (Mg), silver (Ag), nickel(Ni), aluminum (Al), or alloys of these materials.

FIGS. 4A and 4B are plan views of two configurations of first electrodesthat may be used in the first example of electrophoretic display device.

FIG. 4A shows an alternately configured first electrode 510 that may beapplied to an electrophoretic display device, including first patterns510A and second patterns 510B. The first patterns 510A are separated bya plurality of respectively predetermined distances, and the secondpatterns 510B are electrically connected so as to join at least two ofthe mutually separated first patterns 510A. The first patterns 510A areformed in a vertical striped configuration by being parallelly disposedto gate lines 110, and the second patterns 510B are formed in ahorizontal striped configuration by being parallelly disposed to datalines 120. A distance d2 between the first patterns 510A is betweenabout 3 to about 10 μm. The widths W2 of the first patterns 510A may beapproximately equal to or less than the distance d2 between theneighboring first patterns 510A.

The length L2 of the second pattern 500B of the first electrode 500 maybe made larger than the size of a contact hole. The second pattern 500Band the thin film transistor may be electrically connected through thecontact hole.

In FIG. 4B, another configuration of a first electrode 520 includesmutually separated first patterns 520A and second patterns 520Bintersecting with the first patterns 520A to form a lattice.

In order to reduce interference in forming an image, the neighboringfirst patterns 520A have a distance d3 therebetween that is betweenabout 3 to about 10 μm, and the length L3 of the first patterns 520A iseither approximately smaller than or equal to the distance d3 betweenthe first patterns 520A. A distance d4 between the neighboring secondpatterns 520B is between about 3 to about 10 μm, and the widths W3 ofthe second patterns 520B are less than or approximately equal to thedistance d4 between the neighboring second patterns 520B.

The electrophoretic film 600, shown in FIG. 2B includes a capsule 630formed of electrophoretic particles 610 and a solvent 620. Theelectrophoretic particles 610 include first particles 610A that reflectincident light and second particles 610B that absorb incident light. Forexample, the first particles 610A may be white particles, and the secondparticles 610B may be black particles. A binder 640 fixes the capsule630 to the electrophoretic film.

First particles 610A may be charged with a first charge, and secondparticles 610B may be charged with a second charge.

The second electrode 700 is disposed on the electrophoretic film 600 andmay be formed of a transparent and conductive material such as indiumtin oxide (ITO) or indium zinc oxide (IZO).

The above-configured electrophoretic display device may be formed with aplurality of separate first electrodes 500, so that the contacting areabetween the first electrodes 500 and the electrophoretic film 600 can bereduced, thereby increasing the voltage holding ratio.

The electrophoretic display device displays an image through themovement of the electrophoretic particles 610 in the electrophoreticfilm 600, by means of an electric field generated between the firstelectrodes 500 and the second electrodes 700.

The first particles 610A may be positively charged, and the secondparticles 610B may be negatively charged, for example. When a positivevoltage is applied to the first electrodes 500, the second electrodes700 adopt a negative electric potential. The negatively charged secondparticles 610B move toward the first electrode 500, and the positivelycharged first particles 610A move toward the second electrode 700. Whenan external light source is incident on the second electrode 700, thefirst particles 610A reflect the light back again through the secondelectrode 700, forming a white image.

Conversely, when a negative voltage is applied to the first electrode500, the second electrode 700 adopts a positive electric potential. Thepositively charged first particles 610A move toward the first electrode500, and the negatively charged second particles 610B move toward thesecond electrode 700. When an external light source is incident on thesecond electrode 700, the black second particles 610B absorb the lightto form a black image.

At least one thin film transistor Tr and a capacitor CP are disposed onthe pixel region. The gate lines 110 are connected to the gate electrode210 of the thin film transistor Tr, and supply a gate signal to the thinfilm transistor Tr. The data lines 120 are electrically connected withthe source electrode 240A of the thin film transistor Tr, and supply adata signal to the thin film transistor Tr. Thus, the thin filmtransistor Tr provides a data signal to the first electrode 500

The gate lines 110 and the gate electrodes 210 protruding from the gatelines are disposed on the substrate 100. The common lines 130 separatedfrom the gate lines 110 and the capacitor lower electrode 150 connectedto the gate lines 130 are disposed on the substrate 100.

A gate insulating layer 200 is disposed on the substrate 100 to coverthe gate electrode 210. The gate insulating layer 200 may be, forexample, a silicon oxide layer, a silicon nitride layer, or a multilayerof the two.

An active layer 230 is disposed on the gate insulating layer 200corresponding to the gate electrodes 210. The active layer 230 may beformed, for example, of a multilayer including a channel layer and anohmic contact layer formed, respectively, of an amorphous silicon and animpurity-doped amorphous silicon.

The data lines 120 may be disposed on the gate insulating layer 200 tointersect with the gate lines 110. A source electrode 240A is disposedon the active layer 230 and electrically connected to the data lines120. Also, a drain electrode 240B is disposed on the active layer 230and separated from the source electrode 240A.

A capacitor upper electrode 150 is disposed on the gate insulating layer200 and electrically connected to the drain electrode 240B.

Thus, the thin film transistor Tr that includes the gate electrode 210,the active layer 230, and source/drain electrodes 240A and 240B, and acapacitor Cp connected to the thin film transistor Tr are disposed onthe pixel region of the substrate 100.

A protective layer 300 is disposed on the gate insulating layer 200 tocover the thin film transistor Tr and the capacitor Cp. The protectivelayer 300 exposes a portion of the drain electrode 240B, forming acontact hole. The protective layer may be formed of benzocyclobutene(BCB), an acrylic-based resin, or a silicon-based resin. The drainelectrode 240B is electrically connected to the first electrode 500through the contact hole.

The width W1 of the second pattern 500B of the first electrode 500 maybe formed larger than the size of the contact hole so that the secondpattern 500B and the drain electrode 240B may be connected through thecontact hole. As described above, the electrophoretic display device iscapable of increasing a voltage holding ratio by reducing the area ofthe first electrode 500 and the contacting area between the firstelectrode 500 and the electrophoretic film 600 within parameters thatmay not cause the device to interfere with an image.

FIGS. 5A and 5B are diagrams of a second example of an electrophoreticdisplay device FIG. 5A is a plan view, and FIG. 5B is a sectional viewFIG. 5A taken along line III-III′. The electrophoretic display devicehas the substantially the same structure as the electrophoretic displaydevice of the first example. Thus, repetitive descriptions of likeelements will be omitted, and the like elements will be given the samenomenclatures and reference numbers as in the first example.

The electrophoretic display device includes a first electrode 530, anelectrophoretic film 600, and a second electrode 700 formed on asubstrate 100.

The first electrode 530 has a plurality of apertures 540 for exposingthe substrate 100. The apertures 540 are formed in a vertical stripedpattern running parallel to the data lines 120. The plurality ofapertures 540 formed in the first electrode 530, reduces the area of thefirst electrode 530. Thus, the contacting area between the firstelectrode 530 and the electrophoretic film 600 may be reduced, toincrease a voltage holding ratio.

The length L4 of the openings is between about 3 to about 10 μm. If thelength L4 of the openings 540 is formed to be less than about 3 μm, thedecrement of the area of the first electrode 530 would be small, so thatthere would be only a small increase the voltage holding ratio. If thelength L4 of the apertures 540 were to exceed about 10 μm, theelectrophoretic particles on the electrophoretic film within theopenings may not move effectively.

The first electrode 530 is electrically connected to the thin filmtransistor Tr formed on the substrate 100, and is driven through thethin film transistor Tr.

FIGS. 6A and 6B are plan views of two configurations of first electrodesthat may used in a display device according to the second example.

A first electrode 550 applicable includes apertures 560 exposing thesubstrate 100 and arranged in a horizontal stripe pattern parallel tothe gate lines 110. The width W4 of the openings 560 is between about 3and about 10 μm, so that image problems on a finished electrophoreticdisplay device may be avoided, while the voltage holding ratio of theelectrophoretic display device is increased.

Another type of first electrode 570, shown in FIG. 6B may havedot-shaped apertures 580 exposing the substrate 100. The apertures 580may be rectangular, circular, oval, or the like.

When the apertures 580 are rectangular, a length L5 and a width W5 maybe between about 3 and about 10 μm, so that image problems on a finishedelectrophoretic display device may be avoided, while the voltage holdingratio is increased.

The electrophoretic display devices in the above-described examplesreduce the contact area between the electrophoretic film and the firstelectrode, so that the voltage holding ratio of the electrophoreticdisplay device is increased. Also, the resistance at the interfacebetween the electrophoretic film and the first electrode can beincreased, so that a leakage current is reduced. Thus, the electricalcharacteristics of the electrophoretic display device are improved.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An electrophoretic display device comprising: a substrate; a gateline on the substrate; a data line being intersected with the gate line,wherein the gate line and the data line form a pixel region; a thin filmtransistor being disposed in the pixel region; a common line beingdisposed latterly with the gate line; a protective layer covering thegate line, the data line, the thin film transistor and the common line;a capacitor upper electrode being connected to a drain electrode of thethin film transistor; a first electrode disposed on the protective layerand including at least one aperture that exposes the substrate; anelectrophoretic film disposed on the first electrode; and a secondelectrode disposed on the electrophoretic film, wherein the capacitorupper electrode overlaps with the first electrode, wherein the capacitorupper electrode and the common line form a capacitor, wherein thecapacitor overlaps with the first electrode, and wherein the firstelectrode is connected with the capacitor upper electrode through acontact hole formed at the protective layer.
 2. The electrophoreticdisplay device according to claim 1, wherein the aperture has a stripedpattern configuration.
 3. The electrophoretic display device accordingto claim 1, wherein the aperture is dot-shaped.
 4. The electrophoreticdisplay device according to claim 1, wherein the aperture has a width ofabout 3 μm to about 10 μm.
 5. The electrophoretic display deviceaccording to claim 1, wherein the aperture has a length of about 3 μm toabout 10 μm.
 6. The electrophoretic display device according to claim 1,further comprising a thin film transistor disposed on the substrate andelectrically connected to the first electrode.
 7. A display device,comprising: a substrate having a pixel region; a gate line on thesubstrate; a data line being intersected with the gate line, wherein thegate line and the data line form a pixel region; a thin film transistorbeing disposed in the pixel region; a common line being disposedlatterly with the gate line; a protective layer covering the gate line,the data line, the thin film transistor and the common line; a capacitorupper electrode being connected to a drain electrode of the thin filmtransistor; a first electrode on the protective layer; a secondelectrode on the first electrode; and an electrophoretic film disposedbetween the first and the second electrode; wherein an area of at leastone of the first electrode or the second electrode is less than an areaof the pixel region, wherein the capacitor upper electrode overlaps withthe first electrode, wherein the capacitor upper electrode and thecommon line form a capacitor, wherein the capacitor overlaps with thefirst electrode, and wherein the first electrode is connected with thecapacitor upper electrode through a contact hole formed at theprotective layer.
 8. The display device of claim 7, wherein the area ofat least one of the first electrode or the second electrode isapproximately equal to half of the area of the pixel region.
 9. Thedisplay device of claim 7, wherein at least one of the first electrodeor the second electrode is patterned with apertures.